Jiangsu Key Laboratory of Coal-based Greenhouse Gas Control and Utilization, China University of Mining and Technology
Key Laboratory of Coalbed Methane Resource & Reservoir Formation Process, Ministry of Education, China University of Mining & Technology
School of Resources and Earth Science, China University of Mining & Technology

阐明超临界CO2与页岩相互作用物质成分和孔隙结构变化对于实现CO2封存和提高天然气产量至关重要。目前有关矿物溶蚀导致的封存空间演化现象已被大量报道，然而对于次生沉淀发育及封堵特征知之甚少，且缺乏理论和实验支撑。利用四川盆地南部下志留统龙马溪组页岩，以超临界CO2(scCO2)−水−页岩反应、扫描电子显微镜(SEM)、低温N2吸附和等温吸附实验为主要研究方法，分析不同反应时长(6～30 d)矿物溶蚀/沉淀特征及其对页岩吸附性能的影响，揭示封存条件下流固界面动力学特征及孔隙结构演化规律。结果表明，反应后样品中钙质和钾质矿物质量分数随时间逐渐减少，溶液中Ca2+和K+离子质量浓度显著升高。反应过程导致方解石矿物显著被溶蚀，同时页岩表面也产生了较多的碳酸盐沉淀。溶蚀作用会扩大原有孔隙空间，造成3.29～4.50 nm孔隙体积增加；沉淀作用会覆盖原生孔隙空间，导致孔体积增量减少。受溶蚀和沉淀作用影响，孔隙表面分形维数D1微弱增大，结构分形维数D2则为减小趋势，孔隙非均质性增强。总体而言，溶蚀作用会造成样品封存空间增大，导致更多的CO2分子被极化，scCO2流体与页岩相互作用相应增强，这是吸附量和吸附势增大的主要原因；沉淀作用前后样品吸附量和吸附势未发生显著变化，说明沉淀作用对页岩封存能力影响较弱。研究溶蚀和沉淀机制及其对封存空间的影响，对于实现高效、长期的CO2地质封存有重要启示作用。

Understanding the material composition and pore structure variation of shale gas reservoirs during supercritical CO2-shale interaction is of essence to achieve CO2 sequestration and enhanced natural gas production. The storage space evolution associated with mineral corrosion has been well reported, but the studies on the secondary precipitation and plugging characteristics are still insufficient, and there is particularly a lack of theoretical and experimental investigations. To analyze mineralogical corrosion/precipitation characteristics and its effects on adsorption capacity with different reaction time (6‒30 days) and thus demonstrate the fluid-solid interface kinetics and evolution laws of pore structure, the supercritical CO2 (scCO2)-water-shale reaction, scanning electron mi-croscope (SEM), low-pressure N2 adsorption and isothermal adsorption experiments were primarily conducted using the Lower Silurian Longmaxi shales in the southern Sichuan Basin. The results reveal that the content of calcium and potassium minerals in the sample after the reaction gradually decreases with time, leading to an increase of Ca2+ and K+ concentration in the solution. Calcite minerals are notably corroded across the reaction, accompanied by a number of carbonate precipitates that converge on the surface. Corrosion generally expands the initial pore space, resulting in a volumetric increase of pores ranging from 3.29 to 4.50 nm. But the precipitation process may lead to pore space plugging and correspondingly shrinks the increments of the pore volume. As a result of corrosion and precipitation, the surface fractal dimension D1 increases slightly, while the structure fractal dimension D2 shows a reducing trend, which intensifies pore heterogeneity. In general, mineralogical corrosion can enlarge the samples’ storage space, initiate more CO2 molecules to be polarized, and thus strengthen interactions between scCO2 fluids and shale. These are the main reasons for the enhancement of adsorption capacity and adsorption potential. There is no remarkable change in the adsorption and adsorption potential of the sample before and after precipitation, indicating that the precipitation effect has a minor impact on adsorption capacity. Insights into corrosion and precipitation mechanisms and their effects on storage space are a matter of enlightenment for high-efficiency and long-term CO2 geo-sequestration.

中国矿业大学江苏省煤基温室气体减排与资源化利用重点实验室省创新能力建设专项资金资助项目(2020ZDZZ01B)；中央高校基本科研业务费专项资金资助项目(2020CXNL11)；江苏省自然科学基金青年基金资助项目(BK20221147)

代旭光，王猛，冯光俊，等. 超临界CO2−水−页岩作用矿物溶蚀/沉淀特征及其对页岩吸附性的影响[J]. 煤炭学报，2023，48(7)：2813−2826.

DAI Xuguang，WANG Meng，FENG Guangjun，et al. Mineralogical erosion and precipitation characteristics and their effects on adsorption property of shale during scCO2-H2O-shale interaction[J]. Journal of China Coal Society，2023，48(7)：2813−2826.